An opinionated person who offers (unsolicited and often unwanted) advice on the best way to handle a situation
A person sitting in the back-seat of a car issuing (unsolicited and usually unwanted) instructions to the driver
disapproval If you refer to someone, especially a politician, as a back-seat driver, you disapprove of them because they try to influence a situation that does not concern them. They accused the former prime minister of being a backseat driver
disapproval If you refer to a passenger in a car as a back-seat driver, they annoy you because they constantly give you advice